Chemical vapor deposition technique for depositing titanium silicide on semiconductor wafers

ABSTRACT

Disclosed is a chemical vapor deposition (CVD) method of providing a conformal layer of titanium silicide atop a semiconductor wafer within a chemical vapor deposition reactor. Such includes, a) positioning a wafer within the CVD reactor; b) injecting selected quantities of a gaseous titanium halide, or alternately or in addition thereto a gaseous titanium organometallic precursor, a gaseous compound of the formula Si n  H 2n+2  where &#34;n&#34; is an integer greater than or equal to 2, and a carrier gas to within the reactor; and c) maintaining the reactor at a selected pressure and a selected temperature which are effective for reacting the titanium halide and Si n  H 2n+2  to deposit a film on the wafer, the film comprising a titanium silicide, the method being void of use of high intensity light during processing.

RELATED PATENT DATA

This patent resulted from a continuation-in-part application of U.S.patent application Ser. No. 07/926,754, field Aug. 7, 1992, now U.S.Pat. No. 5,240,730.

TECHNICAL FIELD

This invention relates generally to contact technology in semiconductorwafer processing, and more particularly to the providing of silicidelayers within contact openings for reducing contact resistance.

BACKGROUND OF THE INVENTION

In the processing of integrated circuits, electrical contact must bemade to isolated active-device regions formed within a wafer/substrate.The active-device regions are connected by high electrically conductivepaths or lines which are fabricated above an insulator material, whichcovers the substrate surface. To provide electrical connection betweenthe conductive path and active-device regions, an opening in theinsulator is provided to enable the conductive film to contact thedesired regions. Such openings are typically referred to as contactopenings, or simply "contacts".

As transistor active area dimensions approached one micron in diameter,conventional process parameters resulted in intolerable increasedresistance between the active region or area and the conductive layer. Aprincipal way of reducing such contact resistance is by formation of ametal silicide atop the active area prior to application of theconductive film for formation of the conductive runner. One common metalsilicide material formed is TiSi_(x), where x is predominately "2". TheTiSi_(x) material is typically provided by first applying a thin layerof titanium atop the wafer which contacts the active areas within thecontact openings. Thereafter, the wafer is subjected to a hightemperature anneal. This causes the titanium to react with the siliconof the active area, thus forming the TiSi_(x). Such a process is said tobe self-aligning, as the TiSi_(x) is only formed where the titaniummetal contacts the silicon active regions. The applied titanium filmeverywhere else overlies an insulative, and substantially non-reactiveSiO₂ layer.

Such is illustrated in FIG. 1. Shown is a semiconductor wafer 10comprised of a bulk substrate 12 having an active area 14 formedtherein. An overlying layer 16 of insulating material, predominatelySiO₂ in the form of BPSG, has been provided atop substrate 12 andappropriately etched to form a contact opening 18 to active area 14. Athin layer 20 of titanium is applied over insulating layer 16 andcontacts active area 14. The high temperature anneal step is conductedin an inert environment, such as argon, to react titanium metalcontacting active region 14 into TiSi_(x), thereby forming theillustrated TiSi_(x) region 22. The remaining portion of layer 20 notcontacting region 14 is substantially nonreactive with its underlyinginsulating SiO₂ layer 16, and thereby remains as elemental titaniummetal.

A contact filling material, such as tungsten, is typically applied atopsilicide region 22. Tungsten adheres poorly to TiSi_(x). To overcomethis problem, an intervening layer typically of TiN is interposedbetween silicide region 22 and an overlying tungsten layer. TiN iscommonly referred to as a "glue layer" for the metal tungsten layer.Such can be provided by annealing wafer 10 with titanium layer 20 in anatmosphere which is predominately nitrogen. Under such conditions, thelower portion of layer 20 overlying active region 14 will react with thesilicon to form the TiSi_(x), while the upper portion of layer 20 of thetitanium over contact area 14 and the remaining portion of layer 20 overinsulating material 16 reacts with the nitrogen of the atmosphere toform TiN.

From this point, the predominate conductive material of the runner to beformed is applied. The silicide region 22 which is formed is highlyconductive, and provides less electrical resistance between the runnerand active area 14 than were silicide region 22 not present. Formationof such silicides, and titanium silicide in particular, are described inWolf, et al., "Silicon Processing For The VLSI Era. Vol. 2--ProcessIntegration," pages 143-150.

As device dimensions continue to shrink and the contact openings becomedeeper and narrower, contact walls become vertical and most of the metaldeposition techniques fail to provide the necessary step coverage tocreate adequate contact with the active area 14. Such is illustrated inFIG. 2. There, active area 14a of substrate 12a is shown significantlysmaller than active area 14 in FIG. 1. Correspondingly, a significantlynarrower contact opening 18a is provided to active area 14, therebymaximizing circuit density. As is apparent, the ratio of the depth ofcontact opening 18a relative to its width is greater than the ratio ofthe depth to the width of contact opening 18 in FIG. 1. Such narrow,high aspect ratio contact openings 18a can result in layer 20a failingto make significant contact with region 14a, as shown. Accordingly, thedesired TiSi_(x) and electrical contact are not formed,

TiSi_(x) can be deposited directly as opposed to a result of substratereaction with elemental titanium. One way is by low pressure chemicalvapor deposition using titanium tetrachloride and silane according tothe following formula:

    TiCl.sub.4 +2SiH.sub.4 →TiSi.sub.2 +4HCl+2H.sub.2 +by-products

Low pressure chemical vapor deposition provides a distinct advantage ofexcellent conformality adequate to achieve desired coverage in highaspect ratio vias or contacts. However, one significant problemassociated with the above reaction is that it is conducted attemperatures above 700° C. to effect the desired reaction. Mostcommercially available chemical vapor deposition reactors are comprisedof aluminum, which has a melting temperature of around 600° C.Accordingly, alternate material and accordingly more expensive chemicalvapor deposition chambers would need to be developed for the abovereaction to prevent reactor meltdown.

Another drawback associated with high temperature deposition of titaniumsilicide films relates to a competing reaction of the TiCl₄ with siliconof the substrate. Such a reaction would compete with the low pressurechemical vapor deposition reaction, resulting in undesirable oruncontrollable consumption of silicon from the substrate.

Another prior art process of providing a titanium silicide film isdisclosed in U.S. Pat. No. 4,568,565. Such discloses use of titaniumhalides and hydrosilicides, also referred to as silanes. However, theprocess requires the use of high intensity light. Such has the drawbackof increasing process complexity, and causes the processor to contendwith attempting to achieve light uniformity throughout the reactor. Suchis not an easy task. Further, step coverage especially within highaspect ratio openings can be poor in light energy CVD processes assidewalls within such openings do not get full exposure to lightEfficiency is also problematical, as is for example evident from col. 7,Ins. 19-28 of such patent.

It would be desirable to overcome these drawbacks.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described below withreference to the following accompanying drawings.

FIG. 1 is a diagrammatic cross sectional view of a prior art wafer, andis discussed in the "Background" section above.

FIG. 2 is a diagrammatic cross sectional view of an alternate prior artwafer, and is discussed in the "Background" section above.

FIG. 3 is a diagrammatic cross sectional view of a semiconductor waferprocessed in accordance with the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This disclosure of the invention is submitted in furtherance of theconstitutional purposes of the U.S. Patent Laws "to promote the progressof science and useful arts" (Article 1, Section 8).

In accordance with the invention, disclosed is a chemical vapordeposition (CVD) method of providing a conformal layer of titaniumsilicide atop a semiconductor wafer within a chemical vapor depositionreactor. The method comprises, a) positioning a wafer within the CVDreactor; b) injecting selected quantities of a gaseous titanium halide,or alternately or in addition thereto a gaseous titanium organometallicprecursor, a gaseous compound of the formula Si_(n) H_(2n+2) where "n"is an integer greater than or equal to 2, and a carrier gas to withinthe reactor; and c) maintaining the reactor at a selected pressure and aselected temperature which are effective for reacting the titaniumhalide and Si_(n) H_(2n+2) to deposit a film on the wafer, the filmcomprising a titanium silicide, the method being void of use of highintensity light during processing. Carrier and/or dilution gases mightalso of course be utilized in the process.

Such a process can be conducted with an energy source provided to thereactor which consists essentially of thermal energy. Alternately,another or added energy source, such as RF or plasma, might be utilized.

The preferred titanium halide is TiCl₄. Others include titaniumtetraboride, titanium tetrafluoride, titanium tetraiodide, andsubhalides. A preferred titanium organometallic precursor comprises acompound of the formula Ti(NR₂)₄, where R comprises a carbon containingradical An example is tetradimethylamido titanium (TDMAT). Such istypically injected into a reactor by bubbling an inert gas, such as He,through TDMAT liquid which vaporizes the TDMAT which is then directedthe reactor. Other techniques for injecting TDMAT gas into reactor wouldinclude atomizing the TDMAT liquid and injecting such liquid into thereactor which would essentially instantly vaporize into TDMAT gas.Another technique for injecting TDMAT gas into the reactor would be toprovide TDMAT in a solid form in the reactor, with the solid formsubliming and thereby injecting TDMAT gas into the reactor. Suchtechniques for providing TDMAT to a reactor are known to people of skillin the art. Alternate examples of organic titanium precursors includetetradiethylamido titanium, bis-cyclopentadienyl titanium diazide andtris-2,2'bipyridine titanium.

Where n=2, the selected temperature for effectively depositing thedesired layer is expected to be as low as about 400° C. Under suchcircumstances, the selected temperature is preferably from about 400° C.to about 800° C. Most preferred is a temperature from about 400° C. toabout 650° C. to overcome problems associated with high depositiontemperatures, such as described in the "Background" section of thisdocument.

Where n=3, the selected temperature for effectively depositing thedesired layer is expected to be as low as about 300° C. Under suchcircumstances, the selected temperature is preferably from about 300° C.to about 800° C. Most preferred is a temperature from about 300° C. toabout 650° C. to overcome problems associated with high depositiontemperatures, such as described in the "Background" section of thisdocument.

The preferred selected pressure for operation would be a low chemicalvapor deposition pressure of less than or equal to about 100 Torr, witha selected pressure of from about 0.5 Torr to about 30 Torr being mostpreferred.

A wide range of volumetric ratios of titanium halide and/or titaniumorganometallic precursor to Si_(n) H_(2n+2) are expected to be usable,such as from 1:100 to 100:1. The preferred volumetric ratio of isexpected to be from about 1:10 to about 10:1. A mixture of gaseouscompounds of the formula Si_(n) H_(2n+2) could also be utilized, such ascombinations of Si₂ H₆ and Si₃ H₈. A flow of carrier gases is alsoprovided to control the gas distribution above the wafer surface toobtain good uniformity of the film deposited across the wafer. Thepreferred carrier gas is a noble gas, such as helium or argon.

Example flow rates for a six liter chemical vapor deposition reactorwould include from about 1 to 30 sccm of titanium halide and/or titaniumorganometallic precursor, with about 15 sccm being most preferred, andfrom about 1-500 standard cubic centimeters per minute (sccm) of theSi_(n) H_(2n+2) compound(s), with about 25 sccm being most preferred.The preferred flow rate of the carrier gas would be from about 100 sccmto about 2000 sccm. The most preferred flow rate is believed to be about500 sccm. Deposition rate of the film under such conditions is expectedto be 500 Angstroms per minute.

Under the above-described conditions, it is expected that the depositedfilm will comprise a combination of titanium silicides, such as of theformula TiSi, TiSi₂, and Ti₅ Si₃, with the quantity of TiSi₂predominating. Exemplary reactions are presented as follows:

    nTiCl.sub.4 +Si.sub.n H.sub.2n+2 →nTiSi+4nHCl+H.sub.2 +by-products

    nTiCl.sub.4 +2Si.sub.n H.sub.2n+2 →nTiSi.sub.2 +4nHCl+2H.sub.2 +by-products

    TiCl.sub.4 +Si.sub.n H.sub.2n+2 →Ti.sub.5 Si.sub.3 +HCl+H.sub.2 +by-products

    TDMAT+Si.sub.2 H.sub.6 →TiSi.sub.2 +organic by-products

    TDMAT+Si.sub.n H.sub.2n+2 →(n/2)TiSi.sub.2 +organic by-products

Example by-products are expected to be SiH₃ Cl, SiCl and SiH₂ Cl₂.Example organic by-products are expected to be (CH₃)₂ NH₂, CH₃ NH₂ andCH₄.

The invention was reduced to practice using flow rates of TiCl₄, Si₂ H₆,and Ar of 5 sccm, 10 sccm and 400 sccm, respectively. Pressure wasmaintained at 20 Torr, and temperature maintained at 530° C. Processtime was 100 seconds. Bulk resistance of the deposited film wasdetermined to be 20 micro-ohms cm. No laser light was utilized duringprocessing, and accordingly no additional light "absorbing gas" isrequired or utilized, such as is disclosed in U.S. Pat. No. 4,568,565,col. 7, lns. 23-28. Accordingly, the invention overcomes the problemsassociated in the prior art with respect to high intensity lightapplication and with respect to high temperatures.

FIG. 3 illustrates a wafer 50 processed in accordance with theinvention. Wafer 50 includes a bulk substrate 52 having an active area54 formed therein. An insulating layer 56, predominately BPSG, has beenprovided and etched to form a contact opening 58. By the above-describedtechnique, a layer 60 of titanium silicide is conformally provided andmakes excellent contact with region 54.

In compliance with the statute, the invention has been described inlanguage more or less specific as to structural and methodical features.It is to be understood, however, that the invention is not limited tothe specific features shown and described, since the means hereindisclosed comprise preferred forms of putting the invention into

effect. The invention is, therefore, claimed in any of its forms ormodifications within the proper scope of the appended claimsappropriately interpreted in accordance with the doctrine ofequivalents.

We claim:
 1. A chemical vapor deposition method of providing a conformallayer of titanium silicide atop a semiconductor wafer within a chemicalvapor deposition reactor, the method comprising the followingsteps:positioning a wafer within the reactor; injecting selectedquantities of a gaseous titanium halide, a gaseous compound of theformula Si_(n) H_(2n+2) where "n" is an integer greater than or equal to2, and a carrier gas to within the reactor; and maintaining the reactorat a selected pressure and a selected temperature which are effectivefor reacting the titanium halide and Si_(n) H_(2n+2) to deposit a filmon the wafer, the film comprising a titanium silicide, the method beingvoid of use of reaction inducing high intensity light during processing.2. The chemical vapor deposition method of claim 1 wherein the titaniumhalide is TiCl₄.
 3. The chemical vapor deposition method of claim 1further comprising providing an energy source to the reactor formaintaining the temperature, the energy consisting essentially ofthermal energy.
 4. The chemical vapor deposition method of claim 1wherein n=2, and the selected temperature is from about 400° C. to about650° C.
 5. The chemical vapor deposition method of claim 1 wherein n=3,and the selected temperature is from about 300° C. to about 650° C. 6.The chemical vapor deposition method of claim 1 wherein the selectedpressure is from about 0.5 Torr to about 30 Torr.
 7. The chemical vapordeposition method of claim 1 wherein n=2, the selected temperature isfrom about 400° C. to about 650° C., and the selected pressure is fromabout 0.5 Torr to about 30 Torr.
 8. The chemical vapor deposition methodof claim 1 wherein n=3, the selected temperature is from about 300° C.to about 650° C., and the selected pressure is from about 0.5 Torr toabout 30 Torr.
 9. The chemical vapor deposition method of claim 1wherein the titanium silicide of the film is predominately TiSi₂.
 10. Achemical vapor deposition method of providing a conformal layer oftitanium silicide atop a semiconductor wafer within a chemical vapordeposition reactor, the method comprising the followingsteps:positioning a wafer within the reactor; injecting selectedquantities of a gaseous titanium organometallic precursor, a gaseouscompound of the formula Si_(n) H_(2n+2) where "n" is an integer greaterthan or equal to 2, and a carrier gas to within the reactor; andmaintaining the reactor at a selected pressure and a selectedtemperature which are effective for reacting the titanium organometallicprecursor and Si_(n) H_(2n+2) to deposit a film on the wafer, the filmcomprising a titanium silicide, the method being void of use of reactioninducing high intensity light during processing.
 11. The chemical vapordeposition method of claim 10 wherein the titanium organometallicprecursor is selected from the group consisting of a compound of theformula Ti(NR₂)₄, where R comprises a carbon containing radical andbis-cyclopentadienyl titanium diazide, or mixtures thereof.
 12. Thechemical vapor deposition method of claim 10 further comprisingproviding an energy source to the reactor for maintaining thetemperature, the energy consisting essentially of thermal energy. 13.The chemical vapor deposition method of claim 10 wherein n=2, and theselected temperature is from about 400° C. to about 650° C.
 14. Thechemical vapor deposition method of claim 10 wherein n=3, and theselected temperature is from about 300° C. to about 650° C.
 15. Thechemical vapor deposition method of claim 10 wherein the selectedpressure is from about 0.5 Torr to about 30 Torr.
 16. The chemical vapordeposition method of claim 10 wherein n=2, the selected temperature isfrom about 400° C. to about 650° C., and the selected pressure is fromabout 0.5 Torr to about 30 Torr.
 17. The chemical vapor depositionmethod of claim 10 wherein n=3, the selected temperature is from about300° C. to about 650° C., and the selected pressure is from about 0.5Torr to about 30 Torr.
 18. The chemical vapor deposition method of claim10 wherein the titanium silicide of the film is predominately TiSi₂. 19.A chemical vapor deposition method of providing a conformal layer oftitanium silicide atop a semiconductor wafer within a chemical vapordeposition reactor, the method comprising the followingsteps:positioning a wafer within the reactor; injecting selectedquantities of a gaseous titanium halide, a gaseous compound of theformula Si_(n) H_(2n+2) where "n" is 2 or 3, and a carrier gas to withinthe reactor; and maintaining the reactor at a pressure of less than orequal to about 100 Torr and at temperature from about 300° C. to about800° C. which are effective for reacting the titanium halide and Si_(n)H_(2n+2) to deposit a film on the wafer, the film comprising titaniumsilicides of the formulas TiSi, TiSi₂ and Ti₅ Si₃, the method being voidof use of reaction inducing high intensity light during processing. 20.A chemical vapor deposition method of providing a conformal layer oftitanium silicide atop a semiconductor wafer within a chemical vapordeposition reactor, the method comprising the followingsteps:positioning a wafer within the reactor; injecting selectedquantities of a gaseous titanium organometallic precursor, a gaseouscompound of the formula Si_(n) H_(2n+2) where "n" is 2 or 3, and acarrier gas to within the reactor; and maintaining the reactor at apressure of less than or equal to about 100 Torr and at temperature fromabout 300° C. to about 800° C. which are effective for reacting thetitanium organometallic precursor and Si_(n) H_(2n+2) to deposit a filmon the wafer, the film comprising titanium silicides of the formulasTiSi, TiSi₂ and Ti₅ Si₃, the method being void of use of reactioninducing high intensity light during processing.